1. Field of the Invention
The present invention relates to a laminated piezoelectric/electrostrictive element.
2. Description of the Related Art
In a laminated piezoelectric/electrostrictive element formed by laminating a piezoelectric/electrostrictive film and an electrode film, for sufficient densification of the piezoelectric/electrostrictive film, it is necessary to fire the piezoelectric/electrostrictive film at a temperature of 1200° C. or higher. For this reason, the electrode film that is fired simultaneously with the piezoelectric/electrostrictive film needs to have thermal resistance capable of withstanding temperatures of 1200° C. or higher. Thus, platinum that may contribute to an improvement in the thermal resistance of the electrode film is often selected as a material for the electrode film fired simultaneously with the piezoelectric/electrostrictive film.
Meanwhile, in order to improve the piezoelectric/electrostrictive properties of the laminated piezoelectric/electrostrictive element, reducing the thickness of the electrode film as an inner-layer electrode is effective.
In conventional techniques, a platinum powder contained in an electrode paste used for formation of the electrode film is pulverized into small particles to reduce the thickness of the electrode film, and a variety of oxides are added to the platinum powder in order to improve the thermal resistance of the electrode film. However, those conventional techniques have the problem that reducing the thickness of the electrode film to 2.0 μm or less reduces the thermal resistance of the electrode film, thereby causing disconnection of the electrode film at the time of simultaneous firing.
One solution that has been suggested to address this problem is to, in addition to adding a variety of oxides to a platinum powder, control the crystallite diameter of the platinum powder to be within the range of 60 nm to 100 nm through thermal treatment, thereby to improve the thermal resistance of the electrode film (Japanese Patent Application Laid-Open Nos. 2006-302848 and 2006-299385).
This solution results in a reduced thickness and improved thermal resistance of the electrode film, but there is still a problem with the piezoelectric/electrostrictive properties greatly changing with time.